Hi Angel,
First, if the tank is newly set up those white particles will be around for a few days or as long as your power head is churning up the sand. I had similar issues with my BioCube29. I have pics of my tank on here and the angle of the head is perfect. Although, how much sand you have on the bottom of the tank is also going to determine this position. For me I have the power head positioned to the longer portion of the nozzel is downward and it is blowing more toward the surface without creating noise. It is also angled slightly to the left (if your looking at it from the front) so the jet pushes the water around the curved glass creating a current that will make it to the other side of the tank. I also added another powehead in my tank to eliviate any "dead zones" so I have a constant current. It takes some patients but I would put all the sand back to where it was adjust the nozzel and then observed it for a while. If it moved just a little sand I was ok with that. Then I would repeat the process till I found my happy place. Good Luck.